Have a mystery that hopefully someone can explain. My understanding is that the signs of high pressure are the flattening of the primer and shallowing of the firing pin hole.

Just had my Sako action re-barreled (Krieger) to 6mm BR which uses small rifle primers. It seems that at even moderate loads, Federal and Remington primers will blow (burn hole at bottom of the firing pin ding) without showing any signs of flattening or shallowing. The firing pin is set at .050 which is within spec. However, if I use CCI primers (BR4) there is no burn-thru but no flattening either at higher loads.

Can this be related to a tight barrel?? Stumped for an answer. Any ideas would be appreciated.

Ron (Scratching My Head In West Virginia)

Only happened to me once when given some S/Rifle primers which turned out to be S/P's.
I would try different brand and see what happens.
Rob T.

If I understand your problem correctly, I had a rifle that started doing this after about 2,000 rds. The problem was combination of weak firing pin spring and worn firing pin hole in the bolt face.

It DOESN'T sound to me like your problem is excess pressure. I think you are talking about a PUNCTURED primer and not a BLOWN. Correct? Two different animals usually.

[ 08-15-2003, 05:31: Message edited by: Pecos45 ]

What Pecos said, your getting pierced primers, check the firing pin.

After reading your post, i had the same thought, pierced primers. It does not sound like pistol primers as they would also be flattened. Does the primer appear to have extruded itself into the firing pin hole? If not, the pin is piercing the primer....

Have stoned the firing pin and restored its original shape and set the depth. This problem occurs with both Remington and Federal primers; would seem unlikely that both these are bad. Have previously used this same batch of Federal primers in my .223. Had created some hot loads in the .223 without the problem I'm experiencing now.

Replaced the firing pin spring several months ago when the action was being used on 22/250. There was no problem then. Some of these loads showed signs of pressure (flattening)

The "blown" primer (my semantics) is one that has a small pin hole at the bottom of the firing pin ding (just above the anvil). Sometimes a small hole will exist at the bottom of the firing pin ding but gas will not leak out. Other times, the firing pin ding is dark from leaking gas. When the leak does occur, the firing pin seems to be etched by the hot gas.

Thanks. Keep those ideas coming.
Ron

MIke,
There is no extrusion. This bolt if pretty tight around the firing pin. When this action was used with 22-250, it never did extrude into the bolt face. The signs of pressure in its prior life were flattening and shallow firing pin ding. Of course, I was using Federal large rifle primers with the 22-250; now using small rifle.

The problem that I'm having with the 6 BR is you never know when working up a load with a Federal or Remington primer when it is about to "blow". No early warning signs of flattening of shallow FP hole. Next thing you know you find a burned out spot at the bottom of the firing pin ding. Once the SOB blows, the firing pin is etched by the hot gasses and the next firing pin hole is irregular at the bottom.

I have tried backing off the bullet jam with no effect.

This has me baffled.
Ron

The CCI primers wouldn't happen to have a thicker/harder surface than the remington/federal ones? Maybe the distance from the surface to the anvil is just a little bit different. Might be worth a call to the respective manufacturers. Just a thought.

lwells

I use the Lapua 6BR case for my 20BR, even though my chamber was cut for Remington BR case. It is a very tight fit the first time around, but Lapua brass is so much better. 6BR Remington BR brass comes primed, and I believe they use 6 1/2's. I think they are too soft. I use Federal's Gold Medal 205M primers and have no problems. Your problem could be a combination of firing pin and too soft of a primer.

Some time ago I had a problem with blown Federal 210 primers, in loads for several different cartridges used in different rifles -- all in loads that I knew should be mild enough to be significantly under max.

Ultimately I took the problem to Federal, and was told that the primers I was using had been exposed to ammonia in such a way as to weaken the brass of the primer. Thus, they were blowing even with relatively mild loads.

I doubt very much that this is your problem, as you are having it with several different primer brands. But it is one additional place to look to as the source of the trouble when you are having blown primers.

I have only ever pierced a couple of primers. They were not that flat looking either. My theory is that when you pierce the primer you are venting the pressure that would normaly flatten it. I don't use Remingtons, so can't speak about them, but Federal primers are quite soft and show pressure sooner than CCI's. Look at your brass in the neck area, does it look scuffed? Does it chamber a round easily with the firing pin removed? Conceivably could be too tight a fit, depending on chamber neck diameter. If you know the reamer dimentions (talk to your smith if not),measure a loaded round at the neck and see if there is a problem there. Lapua 6 br brass is pretty thick in the neck. (I have heard it is too thick for Sako chambers)I probably would also measure the length at the shoulder of a fired case comparing it to a new case just to rule out a headspaceing problem. You might want to post this in the gunsmithing forum to get their views ...ol blue

This problem started many years ago with the .222 Remington. Standard small rifle primers were made for low intensity cartridges. When the .222 Rem came along, the primers started developing pin holes such as you describe because of the thin cups. Manufacturers have compensated by developing thicker cups on selected primers. Your solution is to use Rem 7&1/2, which was developed for the .222 Rem or the CCI that you mentioned. Old problem that still pops up now and then. Hope this helps.

Appreciate all the really great input on this topic. Will try to address some of the issues raised.

IWells: Did check with Federal and they asked for some of the blown primers. Mr. Mike Larsen indicated that Federal primers are a little hotter that CCI which may explain some of the problem. (One of my friends says CCI's chrono faster than Federal; go figure??)

SST: Agree with you 100% about the quality of Lapua brass. The RP brass have very sloppy primer pockets and the necks vary in thichness by as much as .003. Even though I turned the necks, I would have to go down to about .0105 to clean off all the runout. My throat is .271 and I was trying to keep about .003 to .004 total clearance. .... You may have hit on another excellent point. Many of the Remington Primers that blew initially were what came with the brass orginally. As you indicated, these may have been 6 1/2 instead of the 7 1/2 that I have. Only one of my directly-purchased 7 1/2 blew with moderate loads.

LE270: Yes, about 10 blown primers are on there way to Federal. They were quite willing to look into the matter. They did not expect their primers to blow with beginning loads of 3031 as found in Sierra Manual. I explaind that the action worked fine with the old 22-250 barrel even with high pressure loads eliminating some concern about the firing pin and FP hole in the bolt. I still have many of the old 22-250 cases that show flattened primers and shallow firing pin holes but not one has ever blew using either CCI or Federal primers in the action.

Ol BLue: Know what you are talking about when a primer really blows and burns a nice hole in the bottom. They sort of deflate and cave in on themselves. What is a mystery is the there are none of the typical signs leading up to the primer failure as the loads are increased by 0.5 grains of powder. Would expect the flattening to be obvious and let go on the next powder increase; not so. You may see a little flattening on a work up load where the primer has not failed yet but nothing like you normally expect.

As mention earlier, the RP brass necks should not be a problem as they were turned. Even before turning they easily fit in the chamber without binding. Have been resizing by bumping back the shoulder by about .001. Sometime there is a little resistance on bolt closure but that is mostly because of trying to keep the shoulder bumpback to a minimum. Have dismantled the bolt and checked the feel as the bolt cams the case into the chamber. Very mild resistance at the end of the bolt travel.... Did find out that jamming the bullet into the lands by up to .010 does not significantly increase pressure. Ran a test backing off the bullet to .010 short of the lands and the first Federal primer blew again..... Ran a whole series of tests varying the bullet seating from .010 off to .010 jam. Did not see any significant velocity change nor pressure sign changes with the CCI primers.

Here is what I found out today. Following the line of thinking the the barrel may be very tight, I contacted Krieger. (nice folks). Their barrels for 6 mm are .2430 to .2435. The Sierra bullets I'm using are about .2434 at the gas check. If the barrel is minimum spec of .2430, there may be a little extra pressure trying cram the bullet into a small barrel. Have found that Nosler bullets are .2428 to .2430. Will be trying these tomorrow with Federal Primers to see it they blow.

Really appreciate your fine ideas. If you have any other ideas, let's have them. Will let you all know what I find out.
Ron (in Charleston, West "by God" Virginia)

You might evaluate your priming tool and make certain that the primers are not crushed slightly during seating. The CCIs are much tougher and won't crush easily. It is possible that the pin still has a lot of forward momentum during ignition while the primer is coming back, and only the CCIs can take it.

Sabot, am using one of those hand priming tools from K&M. I cannot detect any crushing of the primer; have used this tool many times before on .223 and 22-250. According to the directions, one should seat the primer until the anvil hits bottom and then give a little extra seating.

Everybody,
Tried using Nosler bullets today. As mentioned earlier, these bullets are smallet that Sierras. They are not larger than .2430. The first load of 28.5 gr. 3031, 70 gr. Nosler BT with Federal blew the primer. This is a very mild load. So my theory of the bullet being too large for the bore seems to be going down the tubes as the Noslers are less than or equal to the groove diameter specs. (Maybe the barrel is out of spec.) There are only 4 lands in the barrel and they are .2360. There width is about the same as a 6 groove barrel so the resistance should be less for the bullets; therefore, less pressure.

Go figure. Thanks for the input.
Ron

.236 is normal for Kreiger 6mm. (.237 can be ordered) That's a stumper... I would probably try a different powder just to rule it out as a cause. I use VV135 for light bullets and Varget for heavier. Other than that I would probably start looking for firing pin & spring problems. (as others have mentioned) Good luck... ol blue

Let's go back to your firing pin assembly. My gut tells me that this is a firing pin problem, but not the tip of the pin. How far does the pin protrude past the bolt face when it is in its max forward position? Compare it with other pin protrusions on different centerfire bolts. If it is excessive, the primer surface is driven too far into the pocket and the pin is still exerting force on this surface as the primer is driven back into it under pressure. The pin is holding the primer forward, preventing full flattening, and too much force is working on the small area that the pin occupies. Residual pressure will collapse the overexttended primer surface as the pin retracts and mask the damage, leaving, on occasion, the small burn hole.

Pop a few rimed cases and look at the depth of the pin strike when pressures are vey low. This could also reveal the same problem.

Have tried 28.5 grains 3031 with the smaller Nosler bullets and Federal primers. One shot; one blown primer. Had previously tried 28.3 grains H322. At about powder mid-weight recommendations, primers were rupturing about 50% of time.

Regarding the protusion of the firing pin, with all slack forward the maximum lenght is .050 which is minimum Sako spec, I believe. This compares favorably to my Remington which was .052.

Will be trying some other batch of Federal primers which a friend says he has used successfully with hot loads. Will let you guys know what the outcome is.

Thanks again for all the great input. Lots of good ideas to keep us thinging and looking.
Ron

PROBLEM SOLVED: The solution was to reduce the firing pin protrusion to .040 which is .010 BELOW the manufacturers minimum spec. of .050 to .055. The tip came from:

Chris Bixler
Graf & Sons
Mexico, MO.

Mr. Bixler indicated that the cups on the Federal primers are not tough enough to handle the Sako action without shortening the firing pin to .040.

The apparent signs of pressure of leaks around the primer may have been caused by under pressure. Ran a test last evening using maximum powder loads of 3031 and did not blow the Federal primers nor did they leak with the shortened firing pin. There was very mild flattening which was expected.

One theory that I have is that there is a 34# firing pin spring in the Sako which is greater than the typical Remington. The extra spring force along with the fact that the actual pin is smaller than a Remington, may impact the Federal primers more severely.

Anyhow, I wish to thank all of you that responded. A special plug to Chris Bixler and to Stan at Douglas Barrels for knowing whom to contact to find the solution.

Ron
Charleston, WV

PS: The gun was shooting less than 300's this AM with heavy loads of 8208 powder.